Which description best differentiates microcell corrosion from uniform corrosion?

• A. Localized attack driven by microgalvanic cells on a single area
• B. Uniform removal across the entire surface
• C. Corrosion only occurs under insulating coatings
• D. It only occurs in high humidity

Answer: (C)

Microcell corrosion is a localized form of attack caused by micro-scale galvanic pairs—areas where a small region acts as an anode while nearby regions act as cathodes. This creates concentrated corrosion in a small spot or along a limited area, rather than thinning the entire surface evenly. That localized pattern is what differentiates microcell corrosion from uniform corrosion, which shows uniform material loss across the whole exposed surface.

So the best description is a localized attack driven by microgalvanic cells on a small area. The idea that corrosion occurs only under insulating coatings isn’t accurate—coatings can influence where corrosion happens, but microcell corrosion isn’t confined to coated areas. And high humidity isn’t a defining requirement for microcell corrosion; while moisture can promote corrosion, microcell effects arise from the microstructural electrochemical differences and can occur under various environmental conditions.